1. Technical Field
The present invention is directed to the field of data communication networks. More particularly, the present invention provides a system and method for path protection switching in a ring network.
2. Description of the Related Art
Ring networks are well known in the data communication art. Typical ring systems include Fiber Distributed Digital Interface (xe2x80x9cFDDIxe2x80x9d) rings, token-ring structures, and more recently Synchronous Optical Network (xe2x80x9cSONETxe2x80x9d) rings. A ring network typically includes a plurality of network nodes coupled together by one or more data communication channels (or paths). These network nodes may, in turn, couple to local nodes or networks, or may couple to other ring structures.
In a SONET network, the network nodes are logically connected by a plurality of virtual paths that coexist on the one or more physical network connections that couple the nodes. Each virtual path may include a plurality of virtual channels, wherein each virtual channel transports packets (or cells) that are formatted according to the SONET standard format, which is known as the Synchronous Payload Envelope (xe2x80x9cSPExe2x80x9d). The SPE further defines the data cells as overhead and payload sections. Overhead information is used to maintain the operation and maintenance of the network, whereas payload information represents the deliverable information of the system being transported in the particular virtual channel. The physical network connection spanning the network nodes may include one or more fiber optic connections. In some network topologies, a single fiber carries payload information in both directions around the ring, whereas in others there is one fiber for one sense of direction, and another fiber for the other sense of direction. In a SONET ring network these two senses of direction are typically referred to as the east and west directions of the ring.
One important concept in ring network design is path protection switching. Path protection switching involves sensing when a fault has occured on the ring network and routing data traffic to accomodate the faulty connection. In some ring systems, a separate path protection channel or connection is provided so that if the main data path is severed (or otherwise inoperative), the system switches traffic onto theprotection channel. However, these systems require a separate physical channel between the network nodes, as well as additional hardware to support the path protection channel. Moreover, if the path protection wire (or fiber) is physically routed in proximity to the main connection between the nodes (as is common), then A fault (such as a fiber cut of the main connection from a back-hoe or other heavy machinery) will likely result in the path protection channel being faulty as well.
Another type of path protection switching known as receiver-based protection switching does not involve a separate path protection line as in the system described above, but rather includes special switching circuitry at the receiver of each network node, which is utilized to avoid the faulty path. This type of path protection switching is commonly implemented in SONET Unidirectional Path Switched Rings (xe2x80x9cUPSRxe2x80x9d). A UPSR typically utilizes two optical fibers, one for transporting data in one direction around the ring, and a second for transporting data in the other direction around the ring. FIG. 1, discussed in more detail below, sets forth such a SONET UPSR network.
In a receiver-based path protection switching system, two identical payload streams (data streams) are transmitted along two separate virtual paths connecting two network nodesxe2x80x94the transmitter node and the receiver node. The two paths represent the two directions of transmission from one node to the next, i.e., xe2x80x9ceastxe2x80x9d and xe2x80x9cwest.xe2x80x9d Operationally, the transmitter of a particular virtual channel launches two identical payload streams in either direction (east and west) towards the receiver node. The receiver node receives the two payload streams, compares their relative transmission quality, and switches from one stream to the other (at the receiver node) based on this comparison.
The main problems with this type of path protection scheme are: (1) it is wasteful of bandwidth since it requires doubling the amount of data necessary to transport useful information on the ring network; (2) switching time in response to a fault is relatively slow; and (3) it requires relatively complex circuitry on both the transmitter and receiver sides of the virtual path in order to manage the dual transmissions.
A system and method for path protection switching in ring networks is provided in which the path protection switch occurs at the transmitter node that initiated a particular virtual channel of data packets onto the ring network. A failure in one of the data communication paths of the ring network is detected by the network nodes on either side of the failure. These network nodes then initiate a wrap mechanism that embeds a special feedback wrap indicator flag into packets that are received at the two nodes, and then wraps (or transmits back) these packets (with the feedback indicator) back in the opposite direction towards the transmitter node that initiated the packets onto the ring. Each transmitter node detects whether received packets are associated with virtual channels that it initiated onto the ring, and if so detected, then determine whether the feedback indicator flag is set. If so, then a protection switch occurs at the transmitter node so that additional packets associated with the particular virtual channel are switched in a direction opposite to the failure. A ring continuity mechanism is used to determine when to revert the transmitter nodes back to their prior operating state, and a garbage collection function is also included.
According to one aspect of the invention a method of path protection switching in a ring network is provided. The ring network includes a plurality of network nodes coupled together by one or more data communication paths. The method includes the steps of (1) detecting a faulty condition between two of the network nodes in the ring network; (2) engaging a wrap mechanism at the two network nodes where the faulty condition is detected in order to wrap data packets received at these nodes away from the faulty condition and back towards the transmitter network node that initially transmitted the data packets onto the ring network; (3) detecting the wrapped packets at the transmitter network node; and (4) engaging a path protection switch at the transmitter network node that switches additional packets away from the faulty condition.
According to another aspect of the invention, a method of path protection switching in a ring network, comprising the steps of: detecting a failure at a first network node in the ring network; setting a forward wrap notification indicator in the overhead section of each packet received at the first network node; wrapping the received packets away from the failure and back towards a second network node that initiated the packets onto the ring network; detecting the wrapped packets at the second network node; and switching the transmitter of the second network node so that additional packets are transmitted away from the first network node where the failure exists.
Still another aspect of the invention provides a system for path protection switching in a ring network, the system including: (A) a detector in each of two network nodes for detecting a faulty condition between the nodes; (B) a wrap controller in each of the two network nodes for engaging a wrap mechanism when the faulty condition is detected in order to wrap data packets received at these nodes away from the faulty condition and back towards a transmitter network node that initially transmitted the data packets onto the ring network; (C) a detector at the transmitter network node for detecting the wrapped packets; and (D) a path protection controller at the transmitter network node that switches additional packets away from the faulty condition.
Yet another aspect of the invention provides a method of garbage collection in a ring network, comprising the steps of: (a) detecting an anomalous condition between two nodes in the ring network; (b) if an anomaly is detected, then setting a wrap indicator flag in packets received at the two nodes and wrapping those packets away from the anomaly; and (c) if a packet having a wrap indicator flag set is received at a node that is wrapping packets away from an anomaly, then discarding those received packets.
It should be noted that these are just some of the many aspects of the present invention. Other aspects not specified will become apparent upon reading the detailed description set forth below.
The present invention overcomes the disadvantages of presently known path protection systems and methods and also provides many advantages, such as: (1) optimized for ring structures; (2) does not waste system bandwidth, as in the receiver-based systems; (3) provides fast protection switching; (4) low cost and low complexity; and (5) easily integrates with existing network node devices (such as a SONET add-drop multiplexer).
These are just a few of the many advantages of the present invention, which is described in more detail below in terms of the preferred embodiments. As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the spirit of the invention. Accordingly, the drawings and description of the preferred embodiments set forth below are to be regarded as illustrative in nature and not restrictive.